1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a printer.
2. Description of the Prior Art
In copying machines there sometimes occurs a case in which the power source switch (main switch, door switch, etc.) is cut off before a copying cycle is completed. According to the prior art, in this case, the copying operation is immediately stopped and the copying machine is brought into its rest position at once by cutting off the power current lines to the loads which otherwise would complete the copying operation. This is common to many of the conventional copying machines hitherto known. However, such a type of copying machine has various disadvantages.
Since data of copying conditions originally set, such as the number of copy sheets, are all cancelled also by switching off during the operation of a copying cycle as mentioned above, difficulties arise at the time of restart of the stopped copying operation. This is true in particular when a number of copies should be made continuously.
If the copying operation is restarted with a copying sheet left in the mechanism and accidentally jammed, it will increase the trouble.
For a transfer type of copying machine, such an interruption of copying operation as mentioned above often makes it impossible to restart the copying operation without trouble. This is because the photosensitive drum may be left alone for a long time in the position in which the potential distribution on the drum surface is very irregular.
It is also known how to clear the copy condition data after the stop of all of the copying operations. However, since all of the copying operations are stopped, the restart of copying cannot be done smoothly. Also, clearance of all of the copy condition data prevents a problemless restart of copying operation.
In making copies, it is often wished that another original document should be urgently copied during a multiple copy operation. In this case, the multiple copy operation proceeding at that time is interrupted for the time being and the remainder of the copy making process is carried out after the urgent copy has been made. Such urgent copy is usually called "interruption copy" in the art. Interruption copy is very troublesome and time consuming. The operator has to calculate and memorize the number of copies to be made after the end of the interruption copying operation. In particular when a large number of copies have to be made as interruption copy, when the sheet size used for the interruption copying is different from that used for the previously started multiple copying, or when an interruption copying sheet is jammed in the machine, the operator is put to great annoyance.
Generally, on the operation panel of a copying machine there are provided a copy botton for giving a copy start instruction, a dial for setting the number of copies wished to be made, an indicator for indicating the number of copies already made and alarm indicator tube for giving notice of occurrance of jam. A copy button and a dial constitute a switch section, and an indicator and an indicator tube constitute an indication section. These two sections are entirely different in function from each other and therefore arranged independently of one another on the operation panel. Of course, the switch section and the indication section are different from each other also in structure. These facts put a limitation to miniaturization of an operation panel. This prevents a further minimization of the copying machine.
A sequential control system has been employed in a copying machine to control operation loads necessary for processing. For this purpose, the machine contains control circuitry composed of semiconductor devices. However, such control circuitry often brings forth troubles of miscontrol due to a wrong operation and a breaking of the circuitry. Especially, when a computer is used in the control circuitry, a wrong operation of the control circuitry has a great deal of adverse effects on the whole sequences and it is very difficult to recover the copying machine operation.
Such a type of image forming apparatus is well known and widely used in which a platen on which an original is placed or an optical system including a lamp for exposing a fixed original is driven into a reciprocal movement so as to expose and scan the original and the exposed image is formed on a photosensitive medium. In such a type of apparatus there occurs the trouble that the reversal of the motion from forward to backward or from backward to forward is not done properly and the moving member runs against the end of the machine body. In this case, the precisely adjusted optical system gets disordered so that the restart of the apparatus becomes difficult.
A recent advancement in the art has made it possible to make various sizes of copies ranging from a smaller size (format B5) to a larger size (format A3) by a single copying machine. Therefore, use of rough timing to check detection of a jammed copying sheet involves a possibility of misoperation.
Also, it may cause trouble to determine developing time for drum latent image on the basis of rough timing. When copy size is smaller, too much amount of toner is applied and the drum is made dirty.
Also, it is known to develope a latent image by dipping the latent image carrying surface into liquid developer or by brushing the latent image surface with a toner brush. In this case, an additional process component is required to remove excess developer. Otherwise it is impossible to improve the developing ability and to obtain good quality image. This makes the apparatus complicate.
In a copying machine of the type in which liquid developer is used, there often occurs such a trouble that when the copying machine is left standing still for a long time, the liquid developer remained on the surface of the photosensitive medium is dried and solidified. It is difficult to wipe out the solid and at the time of restart of the machine it makes the first sheet of copy dirty. Such trouble may be eliminated by carrying out a long period of thorough pre-cleaning at the time of the machine being restarted. However, thereby the copy speed is decreased considerably.